Antifreeze compositions are additives commonly used to lower the freezing point or increase the boiling point of water. Such additives primarily consist of one or more alcohol and/or glycol-based components. Ethylene glycol is the most commonly used antifreeze component. When added to an internal combustion engine cooling system it affords the engine coolant contained therein freeze and antiboil protection (typically between -37.degree. C. to about 115.degree. C., depending on the pressure).
It is known that from the time the antifreeze is added to an aqueous-based engine cooling system the glycol and/or alcohol-based components of the antifreeze start to break down chemically into various organic acids and aldehydes. The organic acids produced are usually glycolic, formic, and to a lesser extent oxalic acids. The breakdown is confirmed by the pH of a traditional phosphate/borate based engine coolant composition decreasing from a pH of about 10.0 downward toward a pH of 7.0. As the pH decreases, corrosion proceeds at a very rapid rate. The less noble metals, such as steel, iron, and cast iron in a coolant system, are the first to go into solution via the corrosion process. Low pH also causes aluminum pitting which readily weakens the wall thickness of its respective components. Copper likewise corrodes and goes into solution. Zinc, used to strengthen silver solder in radiators, leaches out and weakens the solder so that leaks develop. The remaining impurities commonly found are suspended particulate matter primarily corrosion products (metal oxides), dirt, silt, and hard water salt deposits.
To combat the above problems, circulating coolant compositions generally include several known corrosion inhibitors. The inhibitors are added either directly to the coolant or included in an antifreeze solution added thereto which is sold as "inhibited antifreeze". However, a number of commonly accepted corrosion inhibitors have been found to have problems. For example, amines and nitrites are believed to form dangerous nitrosamines when used together. In addition, phosphates have been found to be detrimental to the environment if spent coolant is disposed via waste water treatment systems. Therefore, it is often desirable to have coolants which contain corrosion inhibitors other than nitrites, amines, and phosphates.
An additional problem exists in that, over a period of time, typical corrosion inhibitors such as phosphates, silicates, borates, nitrites, nitrates, azoles, and molybdates are consumed which further contribute to the corrosion effect on the engine system. Furthermore, with time the initial coolant accumulates dissolved impurities and suspended particulate matter and loses effective corrosion inhibition and freeze protection capabilities. For the purpose of replenishing one or more beneficial coolant additives which have been consumed during normal use, supplemental coolant additives (SCA's).are often added to circulating coolants which have been in long term use. Primarily the SCA's are used with heavy duty diesel applications to stop wet sleeve liner pitting (cavitation-corrosion) as well as prevent deposits and scale buildup in the cooling system. Various SCA compositions are disclosed in the following U.S. Pat. Nos.: 3,231,501; 3,962,109; 4,242,214; 4,455,248; 4,564,465; 4,587,028; and 4,588,513 each of which is incorporated in its entirety herein by reference. Typically, such SCA's are added directly to the coolant in the form of a concentrated aqueous solution of the active components of the SCA. For example, diesel truck drivers may be instructed to periodically add defined amounts of such solutions to the cooling systems of their rigs. In certain systems, a solid SCA is included in a circulating coolant filter (see, e.g., U.S. Pat. No. 3,645,402).
Although SCA's may be employed to neutralize degradation products accumulating in the system, these additives are primarily alkaline and include corrosion inhibitors, dispersants, polymers and sequestrants. Generally, however, such compounds do not: restore the depleted antifreeze components (i.e., glycol and/or alcohol); remove the impurities; increase the freeze protection or raise the boiling point of the degraded or used coolant; or inhibit further degradation of the glycol derivative. Therefore, it is generally an accepted practice to remove, replace, and dispose of the coolant composition after a specified period of time.
In many locations, however, antifreeze is considered a hazardous waste and various regulations apply to disposal thereof. In an effort to protect the environment, and as an alternative to disposal, industry continues to develop methods for recycling and reusing such waste products. Examples of such recycling of engine coolants are disclosed in U.S. Pat. Nos. 4,946,595, 4,791,890, 4,793,403, and 5,422,008 (each of which is incorporated herein, in their entirety, by reference). However, reinhibition of recycled antifreeze/coolant formulations presents unique complexities which are substantially different from addition of inhibitors to virgin grade antifreeze/coolant formulations. For example, foaming tendency of recycled glycol can be 20 times greater than that observed for virgin fibre grade ethylene glycol. The unique complexities are due to the chemical and physical characteristics of recycled antifreeze/coolant. Generally, recycled glycol/water solutions contain hard water ions, metal salts, glycol degradation products, and other destabilizing species which can nullify the efficacy of corrosion inhibitors and additives when mixed with inhibitor concentrate. Recycled glycol from spent engine coolant or antifreeze contains heavy metals such as iron, lead, nickel, zinc, and copper. Heavy metals react with and form insoluble salts with corrosion inhibitor anions such as phosphates, borates, silicates, and molybdates. Precipitation causes increased abrasion of cooling system internals, particularly the water pump. Therefore, a need exists for compositions suitable for the replenishment of antifreeze components, such as inhibitors, to the recycled product.
This invention describes a corrosion inhibitor concentrate which may, if desired, be formulated free of nitrites, nitrates, amines, and phosphates. By "concentrate" it is meant that the composition is substantially free of alcohol/glycol-based freezing depressants such as ethylene glycol and propylene glycol. The inhibitor concentrate may subsequently be mixed with the desired freezing depressant in order to formulate a corrosion inhibited coolant composition. The inhibitor concentrate is a "single part" (i.e. it is not necessary to store specified components separately before use), synergistic combination of inhibitors, stabilizers, and antifoam agents, useful for reinhibition of recycled antifreeze/coolant, which are efficacious across a broad range of recycled glycol quality. Furthermore, due to synergy between the essential components of the inhibitor concentrate, the inhibitor concentrate also demonstrates good shelf life. The inhibitor concentrate comprises specific amounts of water, triazole, alkali metal hydroxide, borate, alkali metal silicate, silicate stabilizer, and anti-foaming agent. An additional aspect of this invention includes a process for preparing the inhibitor concentrate.